Researchers from Rutgers University are using nuclear bombs to accurately estimate the age of whale sharks. This is the first time that whale sharks’ age has been properly verified.

Whale sharks can exceed 40 ft and weigh up to 40 tons, according to some estimates. Source: NOAAWhale sharks can exceed 40 ft and weigh up to 40 tons, according to some estimates. Source: NOAA

The team used a measure of lingering radioactivity, also called radiocarbon dating, from nuclear explosions to estimate shark ages. Estimating shark ages help conservationists understand these creatures and create conservation plans. Estimates of longevity, growth and mortality are all important factors in conservation efforts.

Conservationists have found that extended longevity, slow growth rates, late maturity and global connectivity of a species contribute to the whale shark's high susceptibility to human-caused death, like swimming into ship propellers. This helps stakeholders create conservation strategies.

It is difficult to estimate whale shark ages and deaths because the creatures lack the otoliths that scientists use to assess the ages of other fish. But whale shark vertebrae have bands that increase with age, like a tree trunk. Some scientists believe that the rings are added annually, others believe it’s every six months.

During the 1950s and 1960s, the height of the Cold War, nations all over the world tested nuclear weapons in the open air. This temporarily doubled the level of carbon-14 in the atmosphere and increased levels in the ocean. Carbon-14 is a form of carbon and naturally occurring radioactive element. Carbon-14 is frequently used to date ancient bones and artifacts. The increase of carbon-14 in the ocean eventually found its way to the food chain and into the ocean life, leaving lingering levels of carbon-14 in animals.

Researchers can test whale sharks for elevated levels of carbon-14 and date the animals. The team tested whale sharks in Taiwan and Pakistan and were able to date accurately.

The team’s next step is to seek vertebrae of stranded sharks and studying more large and old whale sharks. This would allow scientists to refine growth models, create accurate estimates of growth and natural mortality of whale sharks for conservation efforts.

This study was published in Frontiers of Marine Science.